fuel pressure loss

[fireguyfire]

I did some more trouble shooting on my 76's fuel system yesterday; when performing the leak down test I have fuel pressure drop to zero almost immediately after turning off the fuel pump.
I have gone through and found the accumulator is good, the check valve in the fuel pump is good, so if I understand correctly the only other thing that could be going on to lose fuel pressure that quickly is in the fuel distributor.
Can anyone give me the Coles notes on what it would be inside of the fuel distributor that would be causing this, and more importantly, how to fix it?

[boyt911sc]

Originally Posted by fireguyfire

I did some more trouble shooting on my 76's fuel system yesterday; when performing the leak down test I have fuel pressure drop to zero almost immediately after turning off the fuel pump.
I have gone through and found the accumulator is good, the check valve in the fuel pump is good, so if I understand correctly the only other thing that could be going on to lose fuel pressure that quickly is in the fuel distributor.
Can anyone give me the Coles notes on what it would be inside of the fuel distributor that would be causing this, and more importantly, how to fix it?

FGF,

The PPV (primary pressure valve) inside the FD could leak and cause havoc on your residual fuel pressure. Have you tested the seven (7) fuel injectors for leak?

Tony

[fireguyfire]

No Tony I havent; just went through the testing process to determine where I am losing the pressure and it has to be in the FD.
Just getting together a plan to move forward and fix this issue.
What is your recommended way to test the injectors for fuel pressure loss?
I am guessing by your reply that I should start there before moving on to the primary pressure valve in the FD?


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[boyt911sc]

Originally Posted by fireguyfire

I did some more trouble shooting on my 76's fuel system yesterday; when performing the leak down test I have fuel pressure drop to zero almost immediately after turning off the fuel pump.
I have gone through and found the accumulator is good, the check valve in the fuel pump is good, so if I understand correctly the only other thing that could be going on to lose fuel pressure that quickly is in the fuel distributor.
Can anyone give me the Coles notes on what it would be inside of the fuel distributor that would be causing this, and more importantly, how to fix it?

FGF,

Before you go chasing other suspected components for your sudden residual loss, I would like to know how you tested the FP check valve and the fuel accumulator. If they were tested correctly and verified to be good, then we could proceed to the next most likely culprit. Frequently, the problem is misdiagnosed because of improper test procedure/s specially for those not very familiar with CIS.

It would take me about 15 mins. to test the FP check valve, FA, and FD for residual pressure lost because I have the right set-up and I performed this test very often. I am not underestimating your skill doing the tests but wanted to know how it was done. You won't be here if you know all about these tests.

Share with us the detail of the test and refrain from using adjectives. If you did a pressure test, give as some numbers like 20 psi. for 2 mins. and description of the test. Saying the the check valve is good and fuel accumulator is good is NOT GOOD for my taste. Maybe they passed the tests because it was not tested correctly or done correctly (?). The tests are very simple and easy. You just have to do it the correct way.

Keep us posted.

Tony

[rwest]

Originally Posted by boyt911sc

FGF,

Before you go chasing other suspected components for your sudden residual loss, I would like to know how you tested the FP check valve and the fuel accumulator. If they were tested correctly and verified to be good, then we could proceed to the next most likely culprit. Frequently, the problem is misdiagnosed because of improper test procedure/s specially for those not very familiar with CIS.

It would take me about 15 mins. to test the FP check valve, FA, and FD for residual pressure lost because I have the right set-up and I performed this test very often. I am not underestimating your skill doing the tests but wanted to know how it was done. You won't be here if you know all about these tests.

Share with us the detail of the test and refrain from using adjectives. If you did a pressure test, give as some numbers like 20 psi. for 2 mins. and description of the test. Saying the the check valve is good and fuel accumulator is good is NOT GOOD for my taste. Maybe they passed the tests because it was not tested correctly or done correctly (?). The tests are very simple and easy. You just have to do it the correct way.

Keep us posted.

Tony

Tony,

How should the tests be performed? Do you use the same test rig that is used to test the other CIS pressures?

Thanks,
Rutager

[fireguyfire]

Tony;
Fuel accumulator and fuel pump check valve are both brand new; the accumulated 6 months ago and the new check valve on the fuel pump went in the car this morning.


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[fireguyfire]

I also clamped off the fuel line downstream of the fuel pump after running the pump with a remote switch up to system pressure to test if the leak is forward of the fuel pump; still had a drop in fuel pressure to zero in about 15 seconds with the clamp on the line which tells me the leak is down stream of the pump.


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[fireguyfire]

Sometimes it's best to double check things when trouble shooting, particularly when you have changed one of the variables; because I changed out the fuel pump (which was an original Bosch internal check valve pump) to a brand new fuel pump with the screw in check valve and banjo fitting, I thought I should perhaps rerun my fuel pressure tests to give another benchmarks.

Just finished re running the tests; here is what I got.

All tests performed at 18 degrees C in my shop.
WUR #0438140 033

SYSTEM PRESSURE TEST (valve on gauge towards WUR side closed) 4.9 bar (70 psi)

COLD CONTROL PRESSURE TEST 2.8 bar, or roughly 40 psi

WARM CONTROL PRESSURE TEST (plugged in WUR) no change from cold

RESIDUAL PRESSURE TEST drops to zero in approximately 10 seconds after turning off the FP with the remote switch.

So the only change I have by changing out the fuel pump and check valve is a higher cold control pressure; up from 1.5 bar originally to 2.8 bar.

Again I have done the tests exactly as laid out in the CIS testing for dummies thread in the forum; pulled the red fuel pump relay and have a remote switch wired in which is operating perfectly with the key on.
The last time I got the no change result when plugging in the WUR for the warm control pressure test (with the key "on" and the fuel pump running remotely as described in the how to thread) I got responses saying the car needs to be running to make the WUR work. I have put a bulb tester on the WUR plug leads and with the fuel pump running, key "on" I have no power to the plug; if I start the car I do have power to the plug.

So in summary, I am still chasing the leak that is making it impossible to run a RESIDUAL PRESSURE TEST.
I have a 6 month old accumulator, and a new FP with new FP check valve. My understanding is that everything now points directly to the FD but I thought I would re run the base line tests and post them to get more opinions before continuing.

Tony, is there any other test I can run that would be helpful in figuring out where this massive fuel pressure loss is located?

[fireguyfire]

Should also add the resistance across the leads on the WUR is still 23.6 Ohms.

[Bob Kontak]

Originally Posted by fireguyfire

So in summary, I am still chasing the leak that is making it impossible to run a RESIDUAL PRESSURE TEST.

Can't help myself. You are running a magnificent residual pressure test. You just confirmed you ain't gots no residual pressure. (Why don't I have friends?)

It's odd the control pressure bumped up that much. Was the car stone cold? Existing engine heat can still bend the arm and your numbers are in the range of WCP.

Cool test on the WUR electrical plug. I always wondered about that. Thanks.

[fireguyfire]

Car is stone cold; hasn't been driven for days as I have been out of town; changed out the fuel pump this morning


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[fireguyfire]

And you are correct Bob; I guess the residual pressure test is working! Just not the desired result.


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[fireguyfire]

Can someone explain the process of testing my injectors for fuel leakage?


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[boyt911sc]

Originally Posted by fireguyfire

Can someone explain the process of testing my injectors for fuel leakage?
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FGF,

Pull all seven (7) fuel injectors with the fuel lines. Place each one in a suitable container. CSV is the 7th injector and you could do it later. Focus on the six (6) which are easy to access. With all the 6 injectors properly secured with collection bottles, test run the FP (use terminal 87a & 30) for several seconds. Watch for any fuel drips or flow from each injector. Next test, with the FP still running, lift the AFS plate for a couple of sec. and release. Watch again for any fuel leak.

Fuel injector leak/s usually don't cause an abrupt pressure drop like what you are having. Lastly, test the CSV for leak. This time, it is more cumbersome to do the test with the engine installed. But should not prevent you from doing the test. I don't think these injectors are causing you the residual pressure loss.

I am more inclined to do the FD test at this point. Keep us posted.

Tony

[fireguyfire]

Tony; thanks for the outline on the injectors test;even though I agree with you that because the fuel pressure loss is so quick it is unlikely the injectors I will still test them to learn, as well as rule them out.
Without being a major pain and back to my original post, can someone outline how I should proceed to test the FD? Sounds like there is a check valve in the FD also?


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[boyt911sc]

Originally Posted by fireguyfire

Tony; thanks for the outline on the injectors test;even though I agree with you that because the fuel pressure loss is so quick it is unlikely the injectors I will still test them to learn, as well as rule them out.
Without being a major pain and back to my original post, can someone outline how I should proceed to test the FD? Sounds like there is a check valve in the FD also?


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FGF,

There is no check valve inside the FD. What you have is a relief valve type that controls the system pressure commonly referred as PPV (primary pressure valve). Isolate the FD and do a pressure test.

Tony

[fireguyfire]

Sorry Tony; I meant a relief valve in the FD.
Again sorry to be a pain, but new to these cars and learning how to trouble shoot the CIS system.
Can someone give the details on how to isolate and pressure test the FD, and what the "normal" expected results would be?
Thanks!

[fireguyfire]

Just curious how to test the pressure relief valve inside of the FD for correct operation

[boyt911sc]

Originally Posted by fireguyfire

Just curious how to test the pressure relief valve inside of the FD for correct operation

FGF,

Do you know where the PPV is located on the FD? If you could remove it, you could inspect the seals. Keep us posted.

Tony

[fireguyfire]

Will do Tony


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